I have been running a pretty rich tune for the past 5000 miles (approximate). On my dyno it reads an air/fuel ratio of 16 up to 3500 rpms. Is this seem like enough to clog my cat converter (free flow)?
86' see mods in profile.
Thanks for any info in andvance

 

running rich WILL kill a cat. The question, which I don't know the answer to is if that number is rich enough.

However, what happens to kill a cat (and no kittah jokes ):

1) It gets physically hit... speed bump, running over things... anything that can damage the matrix inside.

2) raw fuel. it comes out and cools the surface of the cat, causeing it to melt into a mass of stuff.

3) lead additive. this will cause the cat to be totallt blocked in no time flat.

 

If I am reading you right you are running 16-1 a/f ratio. That isn't rich, it's lean, quite lean.

 

And that too will kill the cats (as well as the pistons) due to the increased heat

 

see? I told ya I had no idea what to say about that number.

And yes, way too lean will kill a cat... as TM-96CE said.

 

Cats around my place are typically killed by lead poisoning - assuming the greyhound doesn't get em first!

Carl "the field biologist is showing" Johansson

 

ok well it shouldnt be running that same a/f ratio anymore, i just installed a chip tuned by Alvin last night and the car seems to be running alot better.

ok, im lean if thats the case, Im reading this a/f ratio wrong.
So why is it that the exhaust stinks/stinked so much?
And how can I tell if my cat is damaged? and s this a number that cold damage the cat?
Sorry for so many questions

 

I thought it was "clogging"...not killing. So, my answer is "hair-*****"!

 

The number isn't rich. An A/F of 16:1 is painfully lean. The stoichiometric ratio is 14.7:1.


Cooling causes melting? Now there is an intriguing concept.

RACE ON!!!

 

From what I understand that "sulfer" smell is excess fuel in the cats or mabey lean it could be a bogus moment here

But I do know if it is bad enough and recurring it can be a bad sign.

 

bogus moment?

 

oops. poor choice of words.

and I qualified the 16 number as being something I didn't know the answer to a few posts above.

 

ah I see.

So im assuming there is a good chance that the cat could be damaged.
And the only way to find out is to pull it out and look...

 

Cool cats don't clog!!!! Unless their being cooled by raw fuel

 

Based on your first post. I can tell you that running rich like I was for two years will kill even a high flow cat. By hitting it with a wooden broom handle the vette shop could hear stuff rattling in the CAT. You see I failed my strict Emmissions test and wanted to know why. When they pulled my CAT off, and showed it to me: All the honey comb material that used to be in solid block had turned into fist sized and smaller chunks and were all bunched up at the back of the CAT. Thereby reducing/restricting exhaust flow AND not converting dangerous greenhouse gases to harmless water vapor. With a New CAT and a tuning to a leaner setting, I passed the emmissions test with flying colors -Thanks to Tony's Corvette shop in Gaithersburg Maryland. Running too lean like you are doing will burn holes in your soft pistons as well as burn the valves and valve seats in your soft alum heads. I did that on my Trans AM.

 

Take a look at the results of redman-because he was obviously
dumping raw fuel into his cats he clogged them-if you're doing the same thing-find out WHY-before just throwing $$$ at it and replacing a cat(s) cats are made out of precious metals (at least earlier cats such as ours-platinum-if memory serves correct) a honey comb design! by your ratios-if correct-sounds lean-by your NOSE-sounds rich, be sure!

 

OH! I thought it was a "MISSPOKE". You probably should have qualified the whole post.



A simpler, easier, way would be to check the back pressure.

RACE ON!!!

 

There are three things that will cause a catalytic converter to clog. Ther are, in order of likelyhood, PHYSICAL DAMAGE, POISINING and EXCESS FUEL. A LEAN MIXTURE has no adverse effect on the cats.
I will explain each:

PHYSICAL DAMAGE: 80% of completely clogged cats are caused by them getting hit physically, mostly on speed bumps, or a loose hanger causing them to shake excessively over bumpy roads. Although the membranes inside the catylatic converter are protected by a thermal blanket, technology of the substrates on which the active catalyst is supported has seen great progress. In 1974, ceramic substrates had a density of 200 cells per square inch of cross section (31 cells/square cm) and a wall thickness of 0.012 inch or 12 mil (0.305 mm). By late 1970s, the cell density had increased from 300 to 400 cpsi and wall thickness had been reduced by 50% to 6 mil. Then 400, 600 and 900 cpsi substrates were available and wall thickness had be reduced to 2 mil - almost 0.05 mm. In the the middle of the 1980s, substrates derived from ultra-thin foils of corrosion-resistant steels came on to the market. In the beginning, the foils could be made from material only 0.05 mm thick allowing high cell densities to be achieved. Complex internal structures can now be developed; 800 and 1000 cpsi substrates are available and wall thickness is down to 0.025 mm.
As you can see, depending on what year your car is, the substrate membrane internally can be easily damaged. This is the ONLY thing that will cause chunks to be loose inside your cat. If you hit the cats with something like a broom handle and something rattles, it is from physical damage. ( A rich mixture does not cause the pieces to break apart)

POISENING: This is the second most common cause of clogged cats as the contaminates cannot be burnt so they stick to the substrate membrane and build up to the point of clogging the passages.
Common poisons are : Leaded fuel, silicone, gasket sealers, some fuel additives, loose rust and exhaust paste.
The normal operating tenperature will melt these contaminants and they will clog the passages inside the cats

The following steps will minimise "poisening" the cats.
1. When fitting the catalytic converter, don't use exhaust paste in front of the cat. When the exhaust paste hardens it can break off in small chunks and due to the velocity of the exhaust gases, damage the monolith. Paste can also block the monolith.
2. Always use the correct fuel for your car.
3. Never use a fuel additive without first reading the instructions to find out if it is suitable for use with a catalytic converter. If in doubt, contact the manufacturer of the additive.
4 Use extra care with silicone based sealants around the intake manifold , as these can be sucked into the engine and out the exhause to the cats.
5. Additives in oil that is sucked pass the rings into the compustion chamber and out the exhaust can poisen the cats. Ensure that any oil addetives you add to your oil is compatible with cats.
6. Loose rust reaching the cats cannot pass through the small openings in the honeycomb or between the pellets. Remove loose rust from inside the exhaust pipes ahead of the cats when fitting new cats by tapping the pipes with a hammer and briefly starting the car.

EXCESS FUEL While it is possible to completely block the cats due to excess fuel, the process by which this happens makes this the least likely cause. Excess unleaded fuel by itself does not affect the catalysts within the cats. Excess fuel burning inside the cats can in, rear cases, melt the insides of the cats, however there is usually physical damage to render the pieces small enough to melt.
The reason this is rear is that there are so many warning signs before melting that the problem is ususlly diognosed and corrected, long before the cats are completely plugged.
These warning signs include:
1. The O2 sensor will be the first sign and will throw a code because there is unburnt fuel in the exhaust. The O2 sensor will also send the ECM a message to reduce the amount of fuel from the injectors resulting in a general loss of power from the engine. Unless of course the O2 sensor is bad.
2. If the O2 sensor is bad, and the injectors are dumping, (stuck open) the unburned fuel will reach the cats. Providing your air pump is hooked up to introduce more air (oxygen) into the cats (exhaust), the excess fuel will burn inside the cats. However the high tenps (2500 to 3500 degrees) needed to melt the substrates, which are made of either Ceramic or Metal and is coated with precious metals such as Platinum, Palladium and Rhodium, will usually severely discolor the casing of the cats, damage the floorboards of the car or pass alot of heat into the car, warning you that something is wrong with the cats long before complete clogging from meltdown.
3. If you do not have an airpump the excess fuel from a hung up injector will not burn off inside the cats due to a lack of sufficient oxygen, and it will pass out the exhaust as a gas with a strong smell of gasoline. This will not damage the cats at all.
4. A gradual loss of performance due to partial clogging to the point that there will come a time when you will press the gas and the car will just not go any faster.

LEAN MIXTURE While a lean mixture will result in elevated temperatures within the engine and exhaust, it will never be hot enough to melt the materials within a catalytic converter, which are designed to operate at very hot temperatures (see above). The new materials in cats have allowed car manufacturers to move the cats forward to right next to the exhaust manifold because the hotter they are the better they do the job of removing pollutants. Due to warrenty they would never do this if temperatures that an engine is able to operate at (even when lean) had any chance of melting the innerds of the cats.

I know there are people on this forum that will argue that excess fuel will quickly clog the cats, however my research does not support this theory. This is a slow process that takes some time and has alot of warning signs.

I have also notice that there are many people with genuine questions who want to know how the catalytic converters works and how it affects performance.
I have lots of research on this I can pass on as, being a car nut first, I did a paper on the automotive catalytic converter for my Chemistry finals at university. ( Lots of cool chemistry going on in an internal combustion engine and your cats that I have not mentioned and the cats do an amazing job at what they were designed to do in the 1970,s)

Perhaps I could expand on this and start a new thread if anyone is interested.
Best regards
Jerris

 

I would love to read more! Very interesting stuff, and i know little to nothing about the catalyst reaction with the exhaust/pollutents....

 

I would definitley like to know how the cats works and what makes them last so long versus what kills them early. I have an 86 that felt really sluggish but everything checked out. I unbolted the exhaust and it the popes looked like an ash tray. I started the car for a bit and wow so much buildup coming i could never get it out so I had to replace the entire system. With borla.......yea